The present invention relates generally to optical coherence tomography imaging techniques and, more particularly, to stent strut detection using such techniques.
Coronary artery diseases, such as atherosclerosis, are a leading cause of death in the industrialized world. In particular, atherosclerotic plaques may cause narrowing or blockage of the coronary arteries, resulting in reduced blood supply to the heart tissue, which may sometimes lead to serious results such as heart attacks. Medical imaging techniques have greatly assisted the diagnosis and treatment of such coronary artery diseases. For example, coronary X-ray angiography, computed tomography angiography (CTA), magnetic resonance angiography (MRA), intravascular ultrasound (IVUS), and optical coherence tomography (OCT), have all been used to, for example, identify the different constituents of atherosclerotic plaques in the coronary arteries. Of these techniques, CTA and MRA are desirable since they are non-invasive imaging techniques, however, the low resolution of these techniques has limited their ability to resolve the different constituent parts of atherosclerotic plaques.
OCT is able to achieve much higher resolution than CTA and MRA. However, this technique requires invasive catheterization. More particularly, OCT is a medical imaging technology that is functionally similar to ultrasound (IVUS), but relies on infrared light waves instead of sound. As one skilled in the art will recognize, since the frequency of light is much higher than the frequency of sound waves, OCT systems can produce images having a far greater resolution than ultrasound images. In coronary artery imaging application, the resolution of OCT techniques (on the order of 10 μm) can typically not only differentiate between typical constituents of atherosclerotic plaques, such as lipid, calcium, and fibrous tissue, but can also resolve the thin fibrous cap that is thought to be responsible for plaque vulnerability. OCT systems use, for example, a compact diode light source that may be illustratively interfaced with a catheter, endoscope, laparoscope, and/or a surgical probe using well-known optical fiber techniques to image an anatomical feature of a patient. In operations, OCT systems measure the echo time delay and intensity of reflected/backscattered light from, for example, an anatomical feature of a patient, and use this light to produce images that are two- or three-dimensional data sets.
FIG. 1 shows an illustrative OCT sensor that may be used in accordance with an embodiment of the present invention to image one or more anatomical features of a patient, such as the contours of the coronary arteries of the patient. Referring to FIG. 1, sensor 100 is, for example, connected to a diode light source via line 101 that is used to transmit optical signals to and from sensor 100. Sensor 100 is illustratively passed through a catheter 102 that is, for example, transparent to optical or infrared frequencies or another frequency useful in imaging an anatomical feature. In accordance with an embodiment of the present invention, catheter 102 is illustratively first inserted into an anatomical region to be imaged. Then, sensor 100 is passed through the catheter to a desired initial position, for example to an initial position within a coronary artery to be imaged. One skilled in the art will recognize that, in one illustrative embodiment, sensor 100 may already be present within catheter 102 when the catheter is inserted. Once the sensor 100 is in its initial position, an optical signal of a desired frequency, such as at an optical or infrared frequency, is then passed to the sensor 100 via line 101. The resulting signal is then transmitted to device 103 which is, illustratively, a mirror (e.g., a micro mirror) or a prism that functions to direct the signal in direction 307 toward surface 108 (i.e., the surface to be imaged). When the signal reaches surface 108, a portion of the light is reflected in direction 109. When this reflected portion reaches device 103, it is reflected back in direction 110 along line 101 to image processing equipment for processing the collected data into an image. Techniques for processing image data collected by an OCT sensor are well known. Accordingly, such techniques will not be further described herein.
In many uses, such as when the inner surface of a coronary artery is to be imaged, it is desirable to obtain a cross section image of the artery. In such an implementation, sensor 100 is capable of being rotated in directions 105 about axis 111. Accordingly, as the sensor is rotated, the signal reflected by device 103 will rotate around the surface of the artery at the location of the sensor, and image data is collected around the entire diameter of the surface. Thus, as one skilled in the art will recognize, for each position of sensor 100 within an artery, rotating the sensor will produce a cross section image of the artery at that position. Then, according to the present embodiment, in order to obtain an image of the entire artery, the sensor 100 can be retracted along a known path, and data can be collected for a plurality of cross section images of the artery at different positions.
When a full or partial blockage of coronary arteries is diagnosed, various medical procedures may be used to attempt to re-open the blocked arteries. For example, one such procedure, known as percutaneous transluminal coronary angioplasty (PTCA) may be used to open the blocked artery. In many instances a stent is implanted after the angioplasty to keep the artery open and prevent restenosis (regrowth of the plaque). As one skilled in the art will recognize, stents are small metal scaffolds either made from bare metal or coated with drug to inhibit restenosis. Drug-coated stents can also be used to significantly reduce the occurrence of neointimal hyperplasia (NIH), which is a potential complication resulting from the use of stents whereby the inner layer of the blood vessel thickens, possibly causing the closing of the newly opened blood vessel.